Debugger: Pass system environment to sessions started on command line

Processes started with 'qtcreator -debug binary' got an empty
environment at startup, including no DISPLAY etc.

Change-Id: I0c574a3fa25faf18ddf10a6448b0b82c4f04f751
Reviewed-by: Christian Stenger <christian.stenger@theqtcompany.com>

src/plugins/debugger/debuggerplugin.cpp

@@ -1168,6 +1168,7 @@ bool DebuggerPluginPrivate::parseArgument(QStringList::const_iterator &it,
             rp.displayName = tr("Executable file \"%1\"").arg(rp.executable);
             rp.startMessage = tr("Debugging file %1.").arg(rp.executable);
         }
+        rp.environment = Utils::Environment::systemEnvironment();
         m_scheduledStarts.append(QPair<DebuggerRunParameters, Kit *>(rp, kit));
         return true;
     }